1. Field of the Invention
This invention relates to a motorcycle frame for supporting an engine, and more particularly to a layout for the motorcycle frame which simplifies the routing of an intake passageway for the engine.
2. Description of the Relevant Art
Japanese patent No. 2995192 discloses a motorcycle frame provided with a pair of left and right main frames extending from a head pipe, above an engine and towards a rear of the motorcycle. A pair of left and right pivot plates are arranged in a vertical direction behind the engine and are connected to rear end sections of the main frames. A front end of a rear shock absorber arm is swingably supported at middle sections of the pivot plates.
Each pivot plate is provided with an upper part that extends upwards further than a rear end of the main frame. Further, each upper part is provided with a laterally extending part curving inwards, so as to form a tapered shape when viewed from the rear. An upper part of the rear shock absorber is supported between left and right upper parts closest together.
The background art suffers drawbacks. With the above described structure, the position of the cross member is at substantially the same height as the rear end of the main frame. This means that a space enclosed by left and right pivot plates formed below an upper end rear shock absorber attachment section is vertically segmented by the cross member. However, this space is used for the arrangement of an intake passageway made up of a carburetor, an air cleaner and a connecting tube connecting the carburetor and air cleaner. Also, the rear shock absorber protrudes into this space, which means that it is necessary to maintain a sufficiently large space. If this space is partitioned by the cross member, the layout of these intake passageway components is made extremely difficult. In particular, in the case of mounting a four-cycle engine having a large cylinder head, the position of the intake passageway becomes higher, and so layout is made even more difficult.
It is an object of the present invention to overcome one or more of the drawbacks of the background art.
The present invention has upper ends of left and right pivot pates extending further upwards than a mainframe. A rear cross member is suspended between these upper ends, which means that a space enclosed between the left and right pivot plates lower down than the rear cross member can be kept sufficiently large. The large space makes it easier to arrange an intake passageway and a rear shock absorber in this section. As a result, even if the position of the intake passageway is elevated due to employment of a four-cycle engine, a variety of layouts are possible. It is also possible to use the space, enclosed between the left and right mainframes in front of the rear cross member, as a space for arranging a fuel tank. With the fuel tank so placed, it is possible to use the rear cross member as a support section for the fuel tank.
The rear cross member is suspended between upwardly extending sections formed on upper ends of the left and right pivot plates and at a higher position than rear ends of a mainframe. This arrangement results in maintaining sufficient vehicle rigidity. Further, it is easier to arrange a carburetor and a connecting tube and other components constituting an intake passageway, as well as, a rear shock absorber in this larger space.
By the present invention, it is possible to obtain a vehicle frame with a large degree of freedom with respect to layout of the above described components. By the present invention, a simple structure having upwardly extending sections, extending upwards higher than rear sections of the main frame, are provided on the left and right pivot plates. In the present invention, a position of the rear cross member is changed to a high position, so that the rear cross member is suspended between the two upwardly extending sections. Even if the position of the intake passageway becomes higher, as a result of the cylinder head position jutting out at the top, as with a 4-cycle engine, arrangement of the intake passageway can be made easier.
In the present invention, a space further forward than the rear cross member can be kept as a fuel tank storage space. This arrangement allows for a larger volume fuel tank. Also, by making the rear cross member a fuel tank support member, it is possible to simply and reliably support the fuel tank, even if it has a larger volume.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.